Method for oxidizing hydrocarbons

ABSTRACT

The invention relates to a method for oxidizing hydrocarbons with a hydrogen/oxygen mixture in the presence of a catalyst. The catalyst contains a) a support material which contains titanium and b) silver particles having an average particle size ranging from 0.3 to 100 nm.

This application is a 371 of PCT/EP99/05370, filed Jul. 27, 1999.

The present invention relates to a process for the oxidation ofhydrocarbons on a catalyst containing silver in the presence of ahydrogen/oxygen mixture.

The direct oxidation of ethene to ethene oxide by molecular oxygen iswell known and is used commercially to produce ethene oxide. The typicalcatalyst for this application contains metallic or ionic silver,optionally further modified with different promoters and activators.Most of these catalysts contain a porous, inert catalyst support withsmall surfaces such as alpha aluminium oxide, for example, onto whichsilver and promoters were applied. A review of the direct oxidation ofethene in the presence of supported silver catalysts has been compiledby von Sachtler et al. in Catalysis Reviews: Science and Engineering, 23(1&2), 127-149 (1981).

It is also known that the silver catalysts and the reaction conditionswhich have proved to be favourable for ethene oxide production do notlead to comparably good results in the direct oxidation of higherolefins such as propene (U.S. Pat. No. 5,763,630, U.S. Pat. No.5,703,254, U.S. Pat. No. 5,760,254) and maximum propene oxideselectivities of approx. 50% are achieved. Generally speaking the directoxidations of these higher olefins with molecular oxygen in the gasphase do not take place below 200° C.—even in the presence ofcatalysts—and it is therefore difficult selectively to produceoxidation-sensitive oxidation products, such as epoxides, since thesecondary reactions of these products often proceed more quickly thanthe oxidation of the olefins themselves which are used.

U.S. Pat. No. 4,833,260 describes titanium silicalite catalysts whicheffectively make possible the epoxidation of olefins with the oxidanthydrogen peroxide in the liquid phase. In the silicalites a small partof the lattice silicon is replaced by titanium (U.S. Pat. No.4,410,501). The high cost of hydrogen peroxide as oxidant precludeslarge-scale application.

Titanium silicalite-catalyzed epoxidation with pure oxygen as oxidant issuccessful in the presence of a redox system consisting ofalkylanthrahydroquinone and alkylanthraquinone (EP 526,945).

On titanium silicalites containing metallic platinum, propene oxidationis achieved with low yield (approx. 1-2%) and propene oxideselectivities of 60-70% in the liquid phase by means of an in-situhydrogen peroxide formation with a gas mixture consisting of molecularoxygen and molecular hydrogen (JP-A 92/352771, WO 97/47386, WO 96/023023). Hydrogenations which take place as secondary reactions lead tolarge quantities of propane as a by-product and the fact that this is aliquid phase reaction in which the epoxide which is formed isconcentrated in the liquid phase makes these processes of littleinterest as far as industrial use is concerned.

U.S. Pat. No. 5,623,090 describes a gas phase direct oxidation ofpropene to propene oxide with high selectivity. This is a gold-catalyzedgas phase oxidation with molecular oxygen in the presence of hydrogen.Conventional commercial titanium dioxide, which is coated with finelydispersed gold particles, is used as the catalyst. With identical eductgases, another embodiment uses catalysts in which gold is applied to asupport consisting of isolated titanium sites in a silicon dioxidematrix (WO 9800415 A1; WO 9800414 A 1; WO 9800413 A1). These processesall have the disadvantage of being very expensive because of the goldcontent of the catalyst and are not therefore considered for anindustrial use of products such as propene oxide.

The object of the present invention therefore consisted of providing acatalytic process for the oxidation of hydrocarbons which leads toimproved selectivities, yields and costs.

It has surprisingly been found that this object may be achieved ifhydrocarbons are caused to react in the presence of a hydrogen/oxygenmixture on a catalyst which contains silver and titanium.

The present invention thus relates to a process for the oxidation ofhydrocarbons, wherein a mixture containing at least one hydrocarbon,oxygen and hydrogen is converted on a catalyst which contains silver andtitanium, wherein the catalyst contains a support containing titaniumand silver particles with an average particle size of 0.3 to 100 nm.

In principle the process according to the invention may be applied toall hydrocarbons. The term hydrocarbon is intended to mean saturated orunsaturated hydrocarbons such as alkanes or olefins which may alsocontain heteroatoms such as N, O, P or S. Hydrocarbons from which thoseoxidation products, the partial pressure of which is low enoughconsistently to remove the product from the catalyst are formed, arepreferably oxidized. Unsaturated hydrocarbons with 2 to 20, preferably 2to 10 carbon atoms, particularly ethene, propene, 1-butene, 2-butene,butadiene and pentenes and hexenes are preferred.

The catalyst containing silver contains silver particles which arepreferably applied to a support.

The catalyst containing silver contains fine silver particles withaverage particle sizes of 0.3-100 nm, preferably 0.5-20 nm andparticularly preferably 0.5 to 6 nm. The silver content in the catalystis preferably 0.5-10 wt. %.

Pulverulent and pelletized supports are equally suitable as supportmaterials. Amorphous high-surface support materials with surfaces >50m²/g, preferably >100 m²/g, are preferred, particularly those whichcontain titanium such as titanyl hydrates, zinc oxide hydrate containingtitanium, aluminium oxide containing titan ium, titanium dioxides(anatases) or titanium/silicon mixed compounds such as TiO₂—SiO₂ mixedoxides, titanium silicalites or molecular sieves (zeolites) in whichtitanium is present finely dispersed in a silicon matrix.

In principle any crystal structure of the titanium oxide may be selectedalthough the amorphous titanium dioxide modification and anatase arepreferred. The titanium oxide does not have to be present as purecomponent but may also be present as complex material, e.g. incombination with other oxides (e.g. titanates). According to ourknowledge and without wishing to restrict the invention in any way, thetitanium sites in particular which are chemically bonded to silicaand/or inorganic silicates represent the catalytically active titaniumsites. Furthermore we assume that in active catalysts titanium ispresent bonded to the silica or silicate in the form of the oxide [e.g.—Si—O—Ti(═O)—O—Si—].

The support materials containing silicon according to the inventionadvantageously consist of 50%, preferably of 75% and particularlypreferably of >90% of the dioxide form of the silicon. In addition tosilicon dioxide and silicates the support materials containing siliconaccording to the invention may also contain other oxides, e.g. aluminiumoxide, zirconium oxide etc. Support materials containing silicon with alarge specific surface and a high proportion of surface silanol groupsare preferably used. The specific surface should be at least 1 m²/g,preferably in the range from 25-700 m²/g.

Preferred support materials containing silicon are syntheticallyproduced porous silicon dioxides such as silica gels, precipitatedsilica, precipitated silica gels, silicalites or similar and mixturesthereof for example. Production methods for such synthetically producedsilicas are described in “The Colloid Chemistry of Silica and Silicates(R. G. Iler, Cornell University Press, New York, USA, 1955, ChapterVI)”. Examples of these silicas are pyrogenic silicas which are obtainedby conversion of silicon tetrachloride or fluoride with hydrogen andoxygen (e.g. Cab-o-sils from Messrs Cabot Corporation or Aerosils fromMessrs Degussa).

Crystalline alurninosilicates and silicalites, known as molecularsieves, may also be used as support materials containing silicon.Naturally occurring crystalline silicates may also be used, particularlyserpentine (magnesium silicate), clay minerals such as hectorite(lithium magnesium silicate), kaolin, bentonite and mica minerals suchas phlogopite (aluminium magnesium potassium silicalite) or similarmaterials.

The titanium oxide may be produced on support materials containingsilicon in situ from titanium precursor compounds, e.g. by saturationfrom supernatant liquid (impregnation) and/or with an amount of solventcorresponding to the support's absorption capacity (incipient wetness),deposition precipitation, vapour desposition, and by means of thesol-gel method, but equally well by colloid methods, sputtering orvapour deposition. In the impregnations, titanium precursor compoundswhich can react with the surface silanol groups are advantageously used.

Suitable titanium precursor compounds as catalytic titanium species areknown from the prior art, such as soluble titanium salts (e.g. titaniumhalides, nitrates, sulfates, titanium salts of inorganic or organicacids and titanic acid esters).

Titanium derivatives such as tetralkyl titanates with alkyl groups ofC₁-C₆ such as methyl, ethyl, n-propyl, n-butyl, iso-butyl, tert.-butyletc. or other organic titanium species such as titanyl acetyl acetonate,dicyclopentadienyl titanium dichloride are preferably used.Tetra-n-butyl orthotitanate, titanium acetyl acetonate and titaniumtetrachloride are preferred titanium precursor compounds.

Titanium oxide is also produced in situ by grafting with titanocenechloride on supports containing silicon, optionally in the presence of abase. In this case the (η₅—C₅H₂)₂TiCl₂ reacts with terminal surfacesilanol groups. After grafting, drying and calcination, (═SiO)₃TiOHcomplexes presumably form the dominant titanium species. The supportmaterials containing titanium are coated with silver in the next step.

To increase the surface OH groups the catalysts may also be subjected toa water treatment before titanium coating. In this regard watertreatment means that before titanium application the catalyst is broughtinto contact with liquid water or an aqueous saturated ammonium chloridesolution and/or ammonium nitrate solution, or ion exchange withpolyvalent cations (solution of approx. 2 t, for 3 t, approx. 2 t ions),e.g. the catalyst is suspended in the treatment medium and then dried(at 300° C. for example), or the catalyst is treated with steam at >100°C., preferably at 150 to 450° C., for 1-6 hours. Particularly preferablythe catalyst is treated with steam at 200 to 450° C. for 2-5 hours. Thesurplus water is then removed.

To increase the surface OH groups the catalyst support may also betreated by spray impregnation with water or solutions of ammonium saltsor polyvalent cations and then dried.

The silver may be applied to the support in any manner.

Catalyst preparation is preferably by the impregnation method. Theamount of silver, preferably 0.5-10 wt. %, applied to the supportdepends on the surface, the pore structure and the chemical surfacecondition of the support. Amorphous and crystalline high-surfacematerials (>50 m²/g) such as titanyl hydrates, amorphous zinc oxidehydrate containing titanium, titanium dioxides (anatases) ortitanium/silicon mixed compounds such as TiO₂—SiO₂ mixed oxides,titanium silicalites or molecular sieves in which titanium sites arepresent in isolated form in a silicon dioxide matrix such as titaniumsilicalites (MFI structure; two-dimensional ten ring pore system),Ti-beta and/or Ti—Al beta (three-dimensional twelve ring pore system),Ti-ZSM-5 and/or Ti-ZSM-11 (MFI structure; ten ring channels), Ti-ZSM 12(one-dimensional twelve ring channel system), Ti-ZSM48, Ti-MCM-41(mesoporous) are preferably suitable as support materials for coatingwith silver. Titanyl hydrates and titanium/silicon mixed compounds arepreferred supports. Titanyl hydrates are obtainable by hydrolysis oforganic and inorganic titanium precursors (e.g. treatment of titaniumores). Hydrolysis to the titanyl hydrates may also take place in thepresence of any inert support materials such as mica, silicon dioxide.Subsequent calcination of the support materials in the gas streamcontaining oxygen at 250 to 600° C. is particularly preferred. Thesupport material contains immobilized silver in finely dispersed state.Titanyl hydrates with low titanium(III) contents (0.01-2%) and lowsulfate contents (0.1 and 2 wt. %, preferably 0.2-1.0 wt. %) areparticularly preferred. The sulfate may originate from production suchas the sulfate process, or be added when the support is produced or beapplied subsequently by treating the support with reagents (e.g.sulfuric acid or sodium sulfate). The activity of the catalysts whichcontain silver may be increased slightly (approx. 5-10%) by addingpromoters. Promoters from groups 1, 2, 5 and 13 (IUPAC periodic systemof the elements 1985) particularly potassium, tantalum and/or aluminium,and the lanthanides and actinides, particularly europium, lanthanum andpraseodymium, of the periodic system are advantageously used.Advantageously the promoter content is 0.1-5%, preferably 0.5-3%.

The catalyst containing silver may also be produced by thedeposition-precipitation method, in which an aqueous solution of aninorganic or organic silver compound (silver nitrate, sulfate, fluoride,lactate etc.) is added dropwise to an agitated suspension of thecatalyst support. A solvent which contains water is preferably used.Other solvents such as alcohols may also be used. If this silver saltsolution is mixed with bases (e.g. sodium carbonate, potassiumcarbonate, caesium carbonate or lye or alkaline earth lye) up to a pH of7-9, silver precipitates on the support surface in the form of silveroxohydroxo complexes or as silver hydroxide/silver carbonate. To achievea uniform deposition of ultrafine silver particles, the change in the pHmay be controlled by a slow dropwise addition of this alkaline aqueoussolution. It has been found that the possibility of a digestion of theprecipitate with no agglomeration of the silver compounds is improved byadding a carboxylic acid or a salt (preferably magnesium or sodiumcitrate) during or, better still, after the neutralization of theaqueous solution with an alkaline aqueous solution. When the pH rangeremains at 7-9, there is virtually no reduction of the silver compoundby a carbonylation. On drying, precipitated silver hydroxide or silvercarbonate on the support converts into the silver oxide which decomposesand liberates oxygen when calcined above 200° C. or converts toelementary silver by reduction (e.g. hydrogen, hydrazine). Thenano-scale silver particles created in this way are immobilized on thesupport surface in a uniform and adherent manner.

Alternatively to the deposition precipitation method, the silverparticles may also be applied to the support by incipient wetness,sputtering (e.g. 5 wt. % of silver on titanyl hydrate, titanium dioxideor molecular sieves), chemical vapour deposition or from colloidalsuspensions. A co-precipitation of the support and silver component isalso possible. The support catalysts containing silver produced bydifferent methods differ by their silver particle size. By theimpregnation method, silver particles are obtained which are smallerthan by the deposition precipitation method by a factor of 2-3.

Multiple repetition of the impregnation or deposition precipitationmethod with small quantities of silver (e.g. approx. 1-3 wt. % of silverin each case) is advantageous for the production of the catalystcontaining silver. In the process according to the invention, catalystsare therefore preferred in which silver quantities between 1 and 4 wt.%, preferably 1-2 wt. %, were repeatedly applied to the supportaccording to the described impregnation method after washing and drying.When used in the direct oxidation of propene with molecular oxygen inthe presence of molecular hydrogen, the catalyst produced in this wayaccording to the invention (e.g. 5 wt. % of silver on titanium dioxide)produces propene oxide with yields of 1.5-3% and propene oxideselectivities >95%. Only small quantities of ethane, methane and acetonewere found as by-products (approx. 1 vol. % of by-products related topropene oxide formed).

The activity of the oxidation catalysts may decline slightly over time.These catalysts may be regenerated in the oxygen stream atconventionally 300-600° C., preferably at 300-400° C. Regeneration mayalso be achieved by simply washing these catalysts with water or dilutehydrogen peroxide solutions (approx. 3-10%) at room temperature orhigher temperatures with subsequent drying at 150 to 250° C.

On catalyst preparation a thermal reduction of the silver compounds usedmay take place, e.g. during calcination at temperatures above 200° C.,preferably at 300-400° C.

The process according to the invention may be carried out in the gasphase, in liquid phase or also in supercritical phase at temperaturesbetween 20 and 200° C. and any pressure.

If the oxidation according to the invention is undertaken in liquidphase, work is advantageously carried out at a pressure of 1 to 10 barsand in the presence of solvent. Halogenated solvents such as methylenechloride are suitable as solvent in which the catalyst is suspended.Alcohols, such as methanol, ethanol, isopropanol, tert.-butanol ormixtures thereof, and water are also suitable solvents.

In the process according to the invention the catalyst used and thequantities of gas used are not restricted. In the event of a gas phasereaction the quantities of gas stream through the catalyst bed should beapprox. 0.5 to 20 l/g cat.×h⁻¹ (“space velocity”).

The process according to the invention is implemented in the presence ofthe gases oxygen and hydrogen optionally with the addition of inertgases such as nitrogen, argon, helium or carbon dioxide. Temperaturesbetween 30 and 70° C. (Ag/titanium dioxide systems) or 50-180° C.(Ag/titanium-containing systems) are preferred for propene oxidation.Propene oxide is obtained with a yield of 1.5-3%.

The composition of the reaction mixture, containing at least onehydrocarbon such as propene and oxygen, hydrogen and optionally an inertgas may be varied within a wide range. The process according to theinvention is preferably implemented under “hydrogenation conditions”,which means that only very small quantities of oxygen are used inaddition to an excess of hydrogen. The following gas ratios aretherefore preferably used in the process according to the invention:hydrogen/hydrocarbon/oxygen/nitrogen: 20-80 vol. %/5-30 vol. %/1-10 vol.%/0-50 vol. %. Preferably hydrogen/hydrocarbon/oxygen/nitrogen:40-75%/7-15/3-10%/0-20%. The oxygen which is used for the reaction maybe of diverse origin, e.g. pure oxygen, air or other oxygen/inert gasmixtures.

The process according to the invention provides outstanding partialoxidation selectivities at hydrocarbon conversions of 1-3%. Because ofthe very high selectivities, distinctly fewer by-products are formedthan with conventional oxidation catalysts. The process according to theinvention is particularly preferably suitable for the epoxidation ofolefins, particularly for the epoxidation of propene.

Epoxide selectivities >95% (related to converted olefin) are achievedwith olefin conversions of 1.5 to 3% (related to converted olefin).

The characteristics of the present invention will be illustrated in thefollowing examples with the aid of catalyst preparations and catalytictest reactions.

EXAMPLES Example A Specification for Testing the Catalysts (TestSpecification)

A tubular metal reactor of 10 mm internal diameter and 20 cm length,which was tempered by means of an oil thermostat, was used. The reactorwas supplied with educt gases with a set of four mass flow controllers(hydrocarbon, oxygen, hydrogen, nitrogen). For the reaction 0.5 g ofpulvenilent catalyst was presented at 46° C. (Ag/titanium dioxides)and/or 140° C. (Ag/TiO₂—SiO₂-mixed oxides) and 1 bar overpressure. Theeduct gases were metered into the reactor from above. The standardcatalyst load was 2 l/g cat./h. Propene was selected by way of exampleas “standard hydrocarbon”. To carry out the oxidation reactions, anitrogen-enriched gas stream, denoted consistently as standard gascomposition below, was selected: N₂/H₂/O₂/C₃H₆:15/62/10/12%. Thereaction gases were analyzed quantitatively by gas chromatography. Thegas chromatographic resolution of the individual reaction products tookplace by a combined FID/TCD method in which three capillary columns arepassed through.

FID: HP-Innowax, 0.32 mm internal diameter, 60 m long, 0.25μ filmthickness.

WLD: HP-Plot O, 0.32 mm internal diameter, 30 m long, 20μ film thickness

HP-Plot Molsieve 5 A, 0.32 mm internal diameter, 30 m long, 12μ filmthickness.

Example 1 Oxidation of Propene

Catalyst: 2 wt. % of Ag on Titanyl Hydrate by Impregnation, Calcination.

This example illustrates a preparation according to the invention of asupported silver catalyst. To dissolve 787 mg of silver nitrate (5 wt. %of silver related to support to be used) in 100 ml of water, 11 g oftitanyl hydrate (10 g of dry substance) are added at room temperatureaccompanied by stirring. The suspension is stirred for 1 hour at RT, thesolid is separated and washed once with 20 ml of water. The moist solidis dried for 3 hours at 120° C. and then calcined in the air for 2 hoursat 250° C. and 5 hours at 400° C.

A greyish-white catalyst with 2.1 wt. % of silver (EDX) is obtained.Characterization with Transition Electron Microscopy (TEM) showsnano-scale silver particles with average particle sizes in the rangebelow 3 nm.

A propene conversion of 1.5% was achieved in a test according to thetest specification, at PO selectivities of 94%.

Example 2 Oxidation of Isobutane

Catalyst: 2 wt. % of Ag on Titanyl Hydrate by Impregnation, Calcination.

The catalyst was prepared in the sane way as Example 1.

The catalyst was used for isobutane oxidation according to the testspecification.

Tert.-butanol selectivities of 88% and acetic selectivities of 5% wereachieved in a test according to the test specification, with anisobutane oxide conversion of 1.1%.

Example 3 Oxidation of 1-Butene

Catalyst: 2 wt. % of Ag on Titanyl Hydrate by Impregnation, Calcination.

The catalyst was prepared in the same way as Example 1.

The catalyst was used for 1-butene oxidation according to the testspecification.

Butene oxide selectivities of 93% were achieved in a test according tothe test specification at 1-butene conversions of 1.4%.

Example 4 Oxidation of Propene

Catalyst: 1.4 wt. % of Ag on Titanyl Hydrate by Impregnation,Calcination.

This example illustrates a preparation according to the invention of asupported silver catalyst. Preparation in the same way as Example 1except that 475 mg of silver nitrate (3 wt. % of silver related tosupport to be used) in 100 ml of water were presented.

A greyish-white catalyst with 1.4 wt. % of silver (EDX) is obtained.Characterization with TEM shows nano-scale silver particles with averageparticle sizes below 6 nm.

The catalyst was used for propene oxidation according to the testspecification.

Propene oxide selectivities of 95% were achieved in a test according tothe test specification at propene conversions of 1.1%.

Example 5 Oxidation of Propene

Catalyst: 5 wt. % of Ag on Titanyl Hydrate by Deposition Precipitation,Calcination.

This example illustrates a preparation according to the invention of asupported silver catalyst. 20 g of titanyl hydrate were added at RTaccompanied by stirring to dissolve 1588 mg of silver nitrate in 100 mlof water. The pH is set to 8 with a two-molar NACO₃ solution for silverdeposition precipitation. After the pH has been set the aqueoussuspension is stirred for 0.5 hours, 30 mg of magnesium citrate areadded and stirring is continued for a further 2 hours at RT. The solidis separated and washed twice with 70 ml of demineralized water in eachcase. The moist solid is dried for 1.5 hours at 150° C. and thencalcined in the air for 2 hours at 250° C. and for 5 hours at 400° C.

A greyish-white catalyst with 5 wt. % of silver (EDX) is obtained.Characterization with TEM shows nano-scale silver particles with averageparticle sizes from 2 to 10 nm.

The catalyst was used for propene oxidation according to the testspecification.

Propene oxide selectivities of 94% were achieved in a test according tothe test specification at propene conversions of 0.7%.

Example 6 Oxidation of Propene

Catalyst: 5 wt. % of Ag on Titanyl Hydrate by Sputtering, Calcination.

This example illustrates a preparation according to the invention of asupported silver catalyst.

Technical data: Leybold vapour deposition unit (A 1100); target: PK 200(200 mm diameter); starting pressure: 1×10⁻⁵ mbars; working pressure:1×10⁻³ mbars of argon; flask: 1 l round-bottomed flask with a 110 mmopening at an angle of 70°; rotation: 6 rpm; deposition time: 120 mins;cathode output: 110 W.

15 g of pre-dried (2 hours at 150° C.) titanyl hydrate powder are placedin the flask and sputtered with silver.

The solid is dried for 1.5 hours at 150° C. and then calcined in the airfor 2 hours at 250° C. and for 5 hours at 400° C.

An anthracite-coloured catalyst with 5 wt. % of silver (EDX) isobtained. Characterization with TEM shows nano-scale silver particleswith average particle sizes below 5 nm.

The catalyst was used for propene oxidation according to the testspecification.

Propene oxide selectivities of 93% were achieved in a test according tothe test specification at propene conversions of 1.0%.

Example 7 Oxidation of Propene

Catalyst: 2 wt. % of Ag on TS 1 by Impregnation, Calcination.

This example illustrates a preparation according to the invention of asupported silver catalyst. To dissolve 787 mg of silver nitrate (5 wt. %of silver related to support to be used) in 100 ml of water, 10 g of TS1 are added at room temperature accompanied by stirring. The suspensionis stirred for 1 hour at RT, the solid is separated and washed once with20 ml of water. The moist solid is dried for 3 hours at 120° C. and thencalcined in the air for 2 hours at 250° C. and 5 hours at 400° C.

A grey-white catalyst with 2.0 wt. % of silver (EDX) is obtained.Characterization with TEM shows nano-scale silver particles with averageparticle sizes below 6 nm.

The catalyst was used for propene oxidation at 140° C. according to thetest specification.

Propene oxide selectivities of 94% were achieved in a test according tothe test specification at propene conversions of 0.9%.

Example 8

This example describes the preparation of a catalyst support consistingof the oxides of silicon and titanium which was coated with silverparticles. The catalyst support containing Si and Ti is obtained byimpregnation of silica with titanocene dichloride.

20 g of pyrogenic silicon dioxide (Aerosil 200, Messrs Degussa, 200m²/g) were suspended in a 0.5 ml ammonium nitrate solution, stirred for2 hours at 50° C., filtered off, washed three times with 50 ml of water,dried for 2 hours at 120° C. and 3 hours at300° C.

1568 mg of titanocene dichloride (Messrs Merck) were dissolved in 300 mlof chloroform, 10 g of dry Aerosil 380 (Messrs Degussa, pyrogenicsilicon dioxide, 380 m²/g) added, stirred for 30 minutes, 1867 mg oftriethylamine added, stirred for 120 minutes, suction-filtered andwashed with 50 ml of chloroform, dried at 120° C. and calcined for 3hours at 300° C. and for 1 hour at 500° C.

Coating with silver particles took place in the same way as Example 1.

A grey-white catalyst with 2 wt. % of silver (EDX) was obtained.Characterization with TEM shows nano-scale silver particles with averageparticle sizes in the range below 5 nm.

Propene conversions of 1.1% were achieved in a test according to thetest specification at 140° C. at propene selectivities of 94%.

Example 9

This example describes the preparation of a catalyst support consistingof the oxides of silicon, aluminium and titanium which was coated withsilver particles. The catalyst support containing Si and Ti is obtainedby impregnation of a silicon dioxide/aluminium oxide mixed oxide withtitanocene dichloride.

Preparation was in the same way as Example 8 except that a pyrogenicmixed oxide comprising silicon and aluminium was used instead of Aerosil200 (MOX 170; Messrs Degussa, 1% Al₂O₃/99% SiO₂, 170 m²/g).

A grey-white catalyst with 2 wt. % of silver (EDX) is obtained.Characterization with TEM shows nano-scale silver particles with averageparticle sizes in the range below 5 nm.

Propene conversions of 1.3% were achieved in a test according to thetest specification at 140° C. at propene oxide selectivities of 94%.

What is claimed is:
 1. A catalyst useful for oxidizing hydrocarbonscomprising: (a) a support material comprising titanium; and (b) silverparticles which have an average particle size of from about 0.3 to about100 nm; with the proviso that the catalyst is produced by theimpregnation method.
 2. A method for oxidizing hydrocarbons comprising:oxidizing (i) a hydrocarbon with a hydrogen/oxygen mixture in thepresence of a catalyst, the catalyst comprising silver particles whichhave an average particle size of from about 0.3 to about 100 nm and (ii)a support which comprises titanium; with the proviso that the catalystis produced by the impregnation method.